University of Idaho junior Dylan Mortensen wasn’t sure if she was dreaming when a shadowy figure in all black walked by her room in the dead of night in the off-campus rental house she shared with four close friends.

Sometime after 4 a.m. on Sunday, Nov. 13, 2022, Dylan heard strange noises in the three-story house at 1122 King Road in Moscow and swore she heard a male voice say, “It’s okay. I’m going to help you.”

In her somnolent haze, she thought the man was a firefighter holding what looked to her like a vacuum.

At one point, they made eye contact. 

Dylan had no idea that what was unfolding before her very eyes would become one of the most shocking crimes ever to take place on a college campus.

After a night of panicked texts and unanswered calls to three of her housemates, running for safety to housemate Bethany Funke’s room on the ground floor, at about 11:50 a.m., Dylan asked her Pi Beta Phi “Big” Emily Alandt to come over and check out the house.

Just before noon, Emily’s boyfriend Hunter Johnson, who went upstairs to the second floor ahead of the others, made the most bone-chilling discovery of his life when he found Xana and her boyfriend Ethan Chapin dead of apparent stab wounds in her blood-stained room.

Soon after, police found Kaylee and Maddie violently stabbed to death in Maddie’s room.

New details about what happened inside that house are revealed in an explosive book debuting on July 14, The Idaho Four: An American Tragedy, by James Patterson and Vicky Ward, as well as in a new Prime Video docuseries premiering July 11, One Night in Idaho: The College Murders, and in PEOPLE’s exclusive cover story this week.

Based on hundreds of interviews, the book goes in-depth into the lives of the slain students now known as “The Idaho Four” — shedding new light on what happened that tragic night and the unthinkable scene their friends came upon.

When Hunter got to the top of the stairs in the house, he saw Xana’s bedroom door slightly ajar, according to the book.

Opening the door all the way, he found Xana on the floor, face-up, with blood everywhere, the book says.

For more about the Idaho murders, subscribe now to PEOPLE or pick up this week’s issue, on newsstands Friday.

He saw Ethan in bed, facing the wall, dead from apparent stab wounds.

Turning around, he went downstairs and told Dylan and Bethany, “Call 911. And stay outside,” according to the book.

Returning upstairs, he grabbed a kitchen knife out of a drawer, presumably in case the assailant was still in the house.

Just as he was about to head back into Xana’s room, he heard Emily coming up the stairs and stopped her. “Emily, I don’t think Xana’s going to wake up,” he told her, according to the book.

As Emily went back downstairs, he took Xana and Ethan’s pulses, “knowing already that he’s too late,” the book says.

He checked the closets on the second floor and waited in the living room for police to arrive and said he didn’t know whether Kaylee and Maddie were in the house, but feared the worst.

He didn’t tell Emily or the others exactly what he saw in Xana’s room to protect them. “But he already knows the horrific truth: Xana and Ethan are dead.”

In Dec. 2022, suspect Bryan Kohberger was arrested and charged with four counts of first-degree murder in connection with the quadruple homicides. Maintaining his innocence, he had a not guilty plea entered on his behalf and his trial was set to begin in August.

In a surprise move, on Monday, June 30, the former graduate student, 30, asked to plead guilty to the murders to avoid the death penalty, according to a letter that prosecutors sent to victims’ family members, The New York Times reports.

He is expected to officially enter his plea at a hearing on Wednesday, July 2.

Under the proposed plea deal, if approved by the judge, he would be sentenced to four consecutive life terms in prison.

The Idaho Four: An American Tragedy by James Patterson and Vicky Ward is on shelves July 14 and available now for preorder, wherever books are sold.